U.S. patent application number 16/294286 was filed with the patent office on 2019-06-27 for method, apparatus, and program for determining casting state in continuous casting.
This patent application is currently assigned to NIPPON STEEL & SUMITOMO METAL CORPORATION. The applicant listed for this patent is NIPPON STEEL & SUMITOMO METAL CORPORATION. Invention is credited to Satoshi KOSUGI, Junichi NAKAGAWA, Kensuke OKAZAWA.
Application Number | 20190193146 16/294286 |
Document ID | / |
Family ID | 53757216 |
Filed Date | 2019-06-27 |
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United States Patent
Application |
20190193146 |
Kind Code |
A1 |
KOSUGI; Satoshi ; et
al. |
June 27, 2019 |
METHOD, APPARATUS, AND PROGRAM FOR DETERMINING CASTING STATE IN
CONTINUOUS CASTING
Abstract
A determination apparatus of a casting state in continuous
casting where there are a solidified shell, a mold flux layer, and
a mold being respective thermal conductors between a molten steel
and cooling water for the mold, the determination apparatus
comprising an estimation unit, a calculation unit, and a
determination unit. A computer program for causing a computer to
determine a casting state in continuous casting where there are a
solidified shell, a mold flux layer, and a mold being respective
thermal conductors between a molten steel and cooling water for the
mold.
Inventors: |
KOSUGI; Satoshi; (Tokyo,
JP) ; OKAZAWA; Kensuke; (Tokyo, JP) ;
NAKAGAWA; Junichi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIPPON STEEL & SUMITOMO METAL CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
NIPPON STEEL & SUMITOMO METAL
CORPORATION
Tokyo
JP
|
Family ID: |
53757216 |
Appl. No.: |
16/294286 |
Filed: |
March 6, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15112049 |
Jul 15, 2016 |
10286447 |
|
|
PCT/JP2015/052884 |
Feb 2, 2015 |
|
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16294286 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22D 11/041 20130101;
B22D 11/22 20130101; B22D 11/207 20130101; B22D 11/188 20130101;
B22D 11/202 20130101; B22D 11/055 20130101 |
International
Class: |
B22D 11/20 20060101
B22D011/20; B22D 11/22 20060101 B22D011/22; B22D 11/18 20060101
B22D011/18; B22D 11/041 20060101 B22D011/041; B22D 11/055 20060101
B22D011/055 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2014 |
JP |
2014-017443 |
Claims
1. A determination apparatus of a casting state in continuous
casting where there are a solidified shell, a mold flux layer, and
a mold being respective thermal conductors between a molten steel
and cooling water for the mold, the determination apparatus
comprising: an estimation unit which finds a heat transfer
coefficient .alpha. being a heat flux per a unit temperature
difference between the solidified shell and the mold sandwiching
the mold flux layer and a heat transfer coefficient .beta. between
the molten steel and the solidified shell by using data from a
plurality of temperature sensing units which are embedded in the
mold while shifting positions in a casting direction by solving an
inverse problem, and estimates a solidified shell thickness and a
solidified shell temperature from the heat transfer coefficient
.alpha. and the heat transfer coefficient .beta.; a calculation
unit which sets the heat transfer coefficient .alpha., the heat
transfer coefficient .beta., the solidified shell estimated
thickness, and the solidified shell estimated temperature found by
the estimation unit as solidified state in mold estimation amounts,
and obtains solidified state in mold evaluation amounts from the
solidified state in mold estimation amounts; and a determination
unit which determines whether a normal casting state or an abnormal
casting state by comparing at least one or more kinds of amounts
contained in the solidified state in mold estimation amounts and
the solidified state in mold evaluation amounts obtained by the
calculation unit with allowable limit values which are found based
on at least one or more kinds of amounts contained in the
solidified state in mold estimation amounts and the solidified
state in mold evaluation amounts when the abnormal casting occurred
in a past and stored in an allowable limit value storage unit,
wherein in the mold where widths in a horizontal direction of two
planes which are not adjacent but face each other are equal from
among four planes of mold surfaces which are in contact with a cast
slab through the mold flux layer, two planes whose widths in the
horizontal direction are narrower than the other two planes are
called as short sides, a difference of the heat transfer
coefficients .beta. obtained at the short sides at the same mold
height position is called as a short side .beta. difference, a
difference of solidified shell thicknesses obtained at the short
sides at the same mold height position is called as a short side
shell thickness difference, and the solidified state in mold
evaluation amounts are calculated from at least either the short
side .beta. difference or the short side shell thickness
difference.
2. The determination apparatus of the casting state according to
claim 1, wherein an arbitrary position at 120 mm or more and 175 mm
or less from an upper end of the mold is set to P.sub.1, an
arbitrary position at 340 mm or more and 480 mm or less from the
upper end of the mold is set to P.sub.2, and embedding positions of
the temperature sensing units are provided at intervals of 120 mm
or less within a range from P.sub.1 to P.sub.2, and at least one
point is provided at a position where a distance from a lower end
of the mold is within 300 mm.
3. The determination apparatus of the casting state according to
claim 1, wherein, in the determination unit, occurrence of a
break-out is determined in order to determine whether the normal
casting state or the abnormal casting state.
4. The determination apparatus of the casting state according to
claim 1, further comprising: a data storage unit, wherein
time-series data obtained by setting at least one or more kinds of
amounts contained in the solidified state in mold estimation
amounts and the solidified state in mold evaluation amounts as a
time-series data, is stored together with information of whether or
not the abnormal casting occurred; and wherein the allowable limit
value storing unit stores information obtained by deciding
allowable limit values defining a range regarded to be the normal
casting state based on the time-series data when the abnormal
casting occurred and statistic information including an average and
a standard deviation of the time-series data.
5. The determination apparatus of the casting state according to
claim 1, wherein the solidified state in mold evaluation amount is
a moving average from one second to 15 minutes in the past of at
least either the short side .beta. difference or the short side
shell thickness difference.
6. The determination apparatus of the casting state according to
claim 1, wherein the solidified state in mold evaluation amount is
a minimum value from one second to 15 minutes in the past of at
least either an absolute value of the short side .beta. difference
or an absolute value of the short side shell thickness
difference.
7. The determination apparatus of the casting state according to
claim 4, wherein at least one or more kinds of amounts contained in
the solidified state in mold estimation amounts and the solidified
state in mold evaluation amounts are classified by layers in
accordance with classifications for casting conditions and
measurement values defined in advance, and the statistic
information is at least either the average or the standard
deviation in each group classified by layers.
8. The determination apparatus of the casting state according to
claim 7, wherein the casting conditions and the measurement values
are one or more kinds from among a casting speed, a casting width,
a molten steel temperature, a difference between the molten steel
temperature and a liquidus temperature, and a difference between
the molten steel temperature and a solidus temperature.
9. The determination apparatus of the casting state according to
claim 4, wherein a value where one time or more value of the
standard deviation is added to the average and a value where one
time or more value of the standard deviation is subtracted from the
average are used as the allowable limit values.
10. A computer program for causing a computer to determine a
casting state in continuous casting where there are a solidified
shell, a mold flux layer, and a mold being respective thermal
conductors between a molten steel and cooling water for the mold,
the computer program causing a computer to execute: a first process
of finding a heat transfer coefficient .alpha. being a heat flux
per a unit temperature difference between the solidified shell and
the mold sandwiching the mold flux layer and a heat transfer
coefficient .beta. between the molten steel and the solidified
shell by using data from a plurality of temperature sensing units
which are embedded in the mold while shifting positions in a
casting direction by solving an inverse problem, and estimating a
solidified shell thickness and a solidified shell temperature from
the heat transfer coefficient .alpha. and the heat transfer
coefficient .beta.; a second process of setting the heat transfer
coefficient .alpha., the heat transfer coefficient .beta., the
solidified shell estimated thickness, and the solidified shell
estimated temperature found by the first process as solidified
state in mold estimation amounts, and obtaining solidified state in
mold evaluation amounts from the solidified state in mold
estimation amounts; and a third process of determining whether a
normal casting state or an abnormal casting state by comparing at
least one or more kinds of amounts contained in the solidified
state in mold estimation amounts and the solidified state in mold
evaluation amounts obtained by the second process with allowable
limit values which are found based on at least one or more kinds of
amounts contained in the solidified state in mold estimation
amounts and the solidified state in mold evaluation amounts when
the abnormal casting occurred in a past and stored in an allowable
limit value storage unit, wherein in the mold where widths in a
horizontal direction of two planes which are not adjacent but face
each other are equal from among four planes of mold surfaces which
are in contact with a cast slab through the mold flux layer, two
planes whose widths in the horizontal direction are narrower than
the other two planes are called as short sides, a difference of the
heat transfer coefficients .beta. obtained at the short sides at
the same mold height position is called as a short side .beta.
difference, a difference of solidified shell thicknesses obtained
at the short sides at the same mold height position is called as a
short side shell thickness difference, and the solidified state in
mold evaluation amounts are calculated from at least either the
short side .beta. difference or the short side shell thickness
difference.
Description
[0001] This application is a Divisional of U.S. application Ser.
No. 15/112,049, filed Jul. 15, 2016, which is the U.S. National
Phase of PCT/JP2015/052884, filed Feb. 2, 2015, which claims
priority under U.S.C. 119(a) to Japanese Patent Application No.
2014-017443, filed Jan. 31, 2014, the contents of all of which are
incorporated by reference, in their entirety, into the present
application.
TECHNICAL FIELD
[0002] The present invention relates to a method, an apparatus, and
a program for determining a casting state in continuous casting
where a solidified shell, a mold flux layer, and a mold exist
between a molten steel to mold-cooling water.
BACKGROUND ART
[0003] An outline of a continuous casting equipment is illustrated
in FIG. 19. A molten steel prepared by a steel converter and
secondary refining is put into a ladle 51, and poured into a mold 4
through a tundish 52. The molten steel which is in contact with the
mold 4 is cooled and solidified, transported by rolls 54 while a
casting speed thereof is controlled, and cut into a proper length
by a gas cutting machine 55. In the continuous casting of steel as
stated above, there is a possibility that a fluid state and a
solidified state of the molten steel in the mold 4 incur a casting
stop due to a deterioration trouble of properties of a cast slab.
It is therefore necessary to estimate and control the state in the
mold by online to enable stable casting and to manufacture a cast
slab without defect.
[0004] A cross section of the continuous casting equipment in a
vicinity of a mold is illustrated in FIG. 20. A reference numeral 1
is molten steel, a reference numeral 2 is a solidified shell, a
reference numeral 3 is a mold flux layer, a reference numeral 4 is
a mold, a reference numeral 5 is cooling water, and a reference
numeral 8 is an immersion nozzle.
[0005] As illustrated in FIG. 20, the molten steel 1 is poured from
the immersion nozzle 8 into the mold 4, and a cast slab whose side
surface is solidified is pulled out of a bottom of the mold 4 in a
process of the continuous casting. There are unsolidified parts in
the cast slab in a vicinity of a lower end of the mold 4, and they
are entirely solidified at a secondary cooling part at a lower
layer than the mold 4.
[0006] In an operation of the continuous casting, high-speed
casting is aimed to enable improvement in productivity. However,
when the casting speed is too fast, the solidified shell 2 being
the cast slab which is solidified at the side surface of the mold 4
is pulled outside the mold 4 with insufficient strength, and an
operation trouble called as a break-out is incurred because the
solidified shell 2 is broken and the molten steel 1 outflows in the
continuous casting equipment in an extreme case. Once the break-out
occurs, the operation is stopped to perform removal of the steel
which outflows and is solidified in the equipment and repair of the
equipment, as a result, a lot of time is required to recover the
operation, and there is a large loss.
[0007] There are proposed various casting technologies such as
development of a high-speed casting powder, improvement in a
cooling mechanism of a mold copper plate, and a temperature
management to enable a stable high-speed casting without generating
the operation trouble such as the break-out (Non-Patent Literature
1).
[0008] Besides, there is also proposed a technology in which
soundness of a solidified shell in a mold is diagnosed from
measurement values of mold temperatures or the like, a casting
state is determined whether or not it leads to a break-out to
control a casting speed or the like by using the determination
result. For example, in Patent Literature 1, there is proposed a
detection technology of a restrictive break-out. In this example,
the restrictive break-out is avoided by measuring temperatures by
thermocouples embedded in a mold, capturing a time-series change of
characteristic thermocouple temperatures observed when a shell
fracture occurs resulting that the solidified shell is restricted
to the mold, recognizing a fracture surface of the solidified shell
in the mold, and decreasing a casting speed before the fracture
surface reaches a lower end of the mold.
[0009] However, the break-out is not limited to the restrictive
one, and there are ones each of whose sign of the break-out is
difficult to appear in a temperature waveform representing the
time-series change of the temperature. One of them is a break-out
due to drift. The break-out due to drift is a break-out which
occurs when unexpected circumstances such as drift of a molten
steel flow in the mold 4 or the like occur, a heat quantity over
cooling capacity of the mold 4 is locally applied to the solidified
shell 2 to inhibit a solidification growth, and the solidified
shell 2 with insufficient strength is pulled outside the mold 4. In
the continuous casting, the molten steel 1 is poured from the
immersion nozzle 8 into the mold 4, but there is a case when the
break-out due to drift is induced when erosion of the immersion
nozzle 8 occurs, a discharge port excessively deforms caused by
generated inclusions, for example, during casting. It is difficult
to directly observe a drift phenomenon, and characteristics thereof
are difficult to appear also in the mold temperature waveform
different from the restrictive break-out.
[0010] As a detection technology of the break-out due to drift as
stated above, there are proposed development of technologies such
that it becomes possible to estimate a state in a mold owing to an
inverse problem method where other information such as the casting
speed and a cooling water temperature are taken into account in
addition to the mold temperature, and the occurrence of the
break-out is prevented as described in Patent Literatures 2 to 5.
In Patent Literature 2, there is described the inverse problem
method estimating the solidified state in the continuous casting.
Besides, in Patent Literatures 3 to 5, there is described a method
controlling casting to avoid an operation trouble by using
estimation amounts representing the state in the mold obtained by
the method according to Patent Literature 2. However, in Patent
Literatures 3 to 5, there are proposed a method to determine an
abnormal casting state leading to the break-out and an avoidance
method, but they are not generalized, and a concrete method to
determine allowable limit values to determine the abnormal casting
is not specified. Accordingly, when the technologies described in
Patent Literatures 3 to 5 are actually used, it is often the case
to rely on an experience of an executant. Besides, there is not
referred to cases when there are differences in variations of
estimation results depending on casting conditions, and therefore,
there is a possibility that excessively low allowable limit values
are set.
[0011] Besides, there is also proposed a technology estimating a
heat flux from temperatures measured at a plurality of points in a
mold by using a heat transfer inverse problem method to detect the
break-out (Patent Literature 6).
CITATION LIST
Patent Literatures
[0012] Patent Literature 1: Japanese Laid-open Patent Publication
No. S57-152356 [0013] Patent Literature 2: Japanese Laid-open
Patent Publication No. 2011-245507 [0014] Patent Literature 3:
Japanese Laid-open Patent Publication No. 2011-251302 [0015] Patent
Literature 4: Japanese Laid-open Patent Publication No. 2011-251307
[0016] Patent Literature 5: Japanese Laid-open Patent Publication
No. 2011-251308 [0017] Patent Literature 6: Japanese Laid-open
Patent Publication No. 2001-239353
Non-Patent Literatures
[0017] [0018] Non-Patent Literature 1: Edited by The Iron and Steel
Institute of Japan, "Handbook of Iron and Steel (4th edition)",
published by The Iron and Steel Institute of Japan (2002) [0019]
Non-Patent Literature 2: Nakato or the like, "Tetsu-to-Hagane" Vol.
62, No. 11, Page. 5506 (1976)
SUMMARY OF INVENTION
Technical Problem
[0020] An object of the present invention is to provide a detection
technology of a break-out due to drift with little overdetection
and detection leakage by deciding concrete allowable limit values
regarding amounts containing a solidified shell temperature and a
solidified shell thickness to determine an abnormal state of
continuous casting.
Solution to Problem
[0021] Summary of the present invention to solve the above-stated
problems is as follows.
[0022] [1] A determination method of a casting state in continuous
casting where there are a solidified shell, a mold flux layer, and
a mold being respective thermal conductors between a molten steel
and cooling water for the mold, the determination method
includes:
[0023] a first step of finding a heat transfer coefficient .alpha.
being a heat flux per a unit temperature difference between the
solidified shell and the mold sandwiching the mold flux layer and a
heat transfer coefficient .beta. between the molten steel and the
solidified shell by using data from a plurality of temperature
sensing units which are embedded in the mold while shifting
positions in a casting direction by solving an inverse problem, and
estimating a solidified shell thickness and a solidified shell
temperature from the heat transfer coefficient .alpha. and the heat
transfer coefficient .beta.;
[0024] a second step of setting the heat transfer coefficient
.alpha., the heat transfer coefficient .beta., the solidified shell
estimated thickness, and the solidified shell estimated temperature
found in the first step as solidified state in mold estimation
amounts, and obtaining solidified state in mold evaluation amounts
from the solidified state in mold estimation amounts; and
[0025] a third step of determining whether a normal casting state
or an abnormal casting state by comparing at least one or more
kinds of amounts contained in the solidified state in mold
estimation amounts and the solidified state in mold evaluation
amounts obtained in the second step with allowable limit values
which are found based on at least one or more kinds of amounts
contained in the solidified state in mold estimation amounts and
the solidified state in mold evaluation amounts when the abnormal
casting occurred in a past, and stored in an allowable limit value
storage unit,
[0026] wherein in the mold where widths in a horizontal direction
of two planes which are not adjacent but face each other are equal
from among four planes of mold surfaces which are in contact with a
cast slab through the mold flux layer, two planes whose widths in
the horizontal direction are narrower than the other two planes are
called as short sides,
[0027] a difference of the heat transfer coefficients .beta.
obtained at the short sides at the same mold height position is
called as a short side .beta. difference, a difference of
solidified shell thicknesses obtained at the short sides at the
same mold height position is called as a short side shell thickness
difference, and the solidified state in mold evaluation amounts are
calculated from at least either the short side .beta. difference or
the short side shell thickness difference.
[0028] [2] The determination method of the casting state according
to [1], wherein in the third step, occurrence of a break-out is
determined as the determination of whether the normal casting state
or the abnormal casting state.
[0029] [3] The determination method of the casting state according
to [1] or [2], further includes: a time-series data storing step of
setting at least one or more kinds of amounts contained in the
solidified state in mold estimation amounts and the solidified
state in mold evaluation amounts obtained in the second step as a
time-series data, and storing in a data storage unit together with
information of whether or not the abnormal casting occurred;
and
[0030] an allowable limit value storing step of deciding the
allowable limit values defining a range regarded to be the normal
casting state based on the time-series data when the abnormal
casting occurred and statistic information including an average and
a standard deviation of the time-series data, and storing in the
allowable limit value storing unit.
[0031] [4] The determination method of the casting state according
to any one of [1] to [3], wherein the solidified state in mold
evaluation amount is a moving average from one second to 15 minutes
in a past of at least either the short side .beta. difference or
the short side shell thickness difference.
[0032] [5] The determination method of the casting state according
to any one of [1] to [3], wherein the solidified state in mold
evaluation amount is a minimum value from one second to 15 minutes
in a past of at least either an absolute value of the short side
.beta. difference or an absolute value of the short side shell
thickness difference.
[0033] [6] The determination method of the casting state according
to [3], wherein at least one or more kinds of amounts contained in
the solidified state in mold estimation amounts and the solidified
state in mold evaluation amounts are classified by layers in
accordance with classifications for casting conditions and
measurement values defined in advance, and the statistic
information is at least either the average or the standard
deviation in each group classified by layers.
[0034] [7] The determination method of the casting state according
to [6], wherein the casting conditions and the measurement values
are one or more kinds from among a casting speed, a casting width,
a molten steel temperature, a difference between the molten steel
temperature and a liquidus temperature, and a difference between
the molten steel temperature and a solidus temperature.
[0035] [8] The determination method of the casting state according
to [3], wherein a value where one time or more value of the
standard deviation is added to the average and a value where one
time or more value of the standard deviation is subtracted from the
average are used as the allowable limit values.
[0036] [9] The determination method of the casting state according
to any one of [1] to [8], wherein an arbitrary position at "0"
(zero) mm or more and 95 mm or less downward from a supposed molten
steel surface level position of the mold is set to P.sub.1, an
arbitrary position at 220 mm or more and 400 mm or less downward
from the molten steel surface level position is set to P.sub.2, and
embedding positions of the temperature sensing units are provided
at intervals of 120 mm or less within a range from P.sub.1 to
P.sub.2, and at least one point is provided at a position where a
distance from a lower end of the mold is within 300 mm.
[0037] [10] A determination apparatus of a casting state in
continuous casting where there are a solidified shell, a mold flux
layer, and a mold being respective thermal conductors between a
molten steel and cooling water for the mold, the determination
apparatus includes:
[0038] an estimation unit which finds a heat transfer coefficient
.alpha. being a heat flux per a unit temperature difference between
the solidified shell and the mold sandwiching the mold flux layer
and a heat transfer coefficient .beta. between the molten steel and
the solidified shell by using data from a plurality of temperature
sensing units which are embedded in the mold while shifting
positions in a casting direction by solving an inverse problem, and
estimates a solidified shell thickness and a solidified shell
temperature from the heat transfer coefficient .alpha. and the heat
transfer coefficient .beta.;
[0039] a calculation unit which sets the heat transfer coefficient
.alpha., the heat transfer coefficient .beta., the solidified shell
estimated thickness, and the solidified shell estimated temperature
found by the estimation unit as solidified state in mold estimation
amounts, and obtains solidified state in mold evaluation amounts
from the solidified state in mold estimation amounts; and
[0040] a determination unit which determines whether a normal
casting state or an abnormal casting state by comparing at least
one or more kinds of amounts contained in the solidified state in
mold estimation amounts and the solidified state in mold evaluation
amounts obtained by the calculation unit with allowable limit
values which are found based on at least one or more kinds of
amounts contained in the solidified state in mold estimation
amounts and the solidified state in mold evaluation amounts when
the abnormal casting occurred in a past and stored in an allowable
limit value storage unit,
[0041] wherein in the mold where widths in a horizontal direction
of two planes which are not adjacent but face each other are equal
from among four planes of mold surfaces which are in contact with a
cast slab through the mold flux layer,
[0042] two planes whose widths in the horizontal direction are
narrower than the other two planes are called as short sides,
[0043] a difference of the heat transfer coefficients .beta.
obtained at the short sides at the same mold height position is
called as a short side .beta. difference, a difference of
solidified shell thicknesses obtained at the short sides at the
same mold height position is called as a short side shell thickness
difference, and
[0044] the solidified state in mold evaluation amounts are
calculated from at least either the short side .beta. difference or
the short side shell thickness difference.
[0045] [11] The determination apparatus of the casting state
according to [10], wherein an arbitrary position at 120 mm or more
and 175 mm or less from an upper end of the mold is set to P.sub.1,
an arbitrary position at 340 mm or more and 480 mm or less from the
upper end of the mold is set to P.sub.2, and embedding positions of
the temperature sensing units are provided at intervals of 120 mm
or less within a range from P.sub.1 to P.sub.2, and at least one
point is provided at a position where a distance from a lower end
of the mold is within 300 mm.
[0046] [12] A computer program for causing a computer to determine
a casting state in continuous casting where there are a solidified
shell, a mold flux layer, and a mold being respective thermal
conductors between a molten steel and cooling water for the mold,
the computer program causes a computer to execute:
[0047] a first process of finding a heat transfer coefficient
.alpha. being a heat flux per a unit temperature difference between
the solidified shell and the mold sandwiching the mold flux layer
and a heat transfer coefficient .beta. between the molten steel and
the solidified shell by using data from a plurality of temperature
sensing units which are embedded in the mold while shifting
positions in a casting direction by solving an inverse problem, and
estimating a solidified shell thickness and a solidified shell
temperature from the heat transfer coefficient .alpha. and the heat
transfer coefficient .beta.;
[0048] a second process of setting the heat transfer coefficient
.alpha., the heat transfer coefficient .beta., the solidified shell
estimated thickness, and the solidified shell estimated temperature
found by the first process as solidified state in mold estimation
amounts, and obtaining solidified state in mold evaluation amounts
from the solidified state in mold estimation amounts; and
[0049] a third process of determining whether a normal casting
state or an abnormal casting state by comparing at least one or
more kinds of amounts contained in the solidified state in mold
estimation amounts and the solidified state in mold evaluation
amounts obtained by the second process with allowable limit values
which are found based on at least one or more kinds of amounts
contained in the solidified state in mold estimation amounts and
the solidified state in mold evaluation amounts when the abnormal
casting occurred in a past and stored in an allowable limit value
storage unit,
[0050] wherein in the mold where widths in a horizontal direction
of two planes which are not adjacent but face each other are equal
from among four planes of mold surfaces which are in contact with a
cast slab through the mold flux layer,
[0051] two planes whose widths in the horizontal direction are
narrower than the other two planes are called as short sides,
[0052] a difference of the heat transfer coefficients .beta.
obtained at the short sides at the same mold height position is
called as a short side .beta. difference,
[0053] a difference of solidified shell thicknesses obtained at the
short sides at the same mold height position is called as a short
side shell thickness difference, and
[0054] the solidified state in mold evaluation amounts are
calculated from at least either the short side .beta. difference or
the short side shell thickness difference.
Advantageous Effects of Invention
[0055] According to the present invention, it is possible to decide
concrete allowable limit values regarding amounts containing a
solidified shell temperature and a solidified shell thickness to
determine an abnormal state of continuous casting, and therefore,
executors are able to decide the allowable limit values independent
from experiences. It is thereby possible to provide a detection
technology of a break-out due to drift with little overdetection
and detection leakage to improve accuracy of a state determination
of a casting state. Occurrence of operational accidents such as a
break-out due to drift is therefore prevented, and it contributes
to improvement in productivity by relaxing restriction in a casting
speed which is set so as to avoid the operational accidents.
BRIEF DESCRIPTION OF DRAWINGS
[0056] FIG. 1 is a flowchart illustrating a determination method of
a casting state according to an embodiment.
[0057] FIG. 2 is a view illustrating a part of a cross section in a
vicinity of a mold of a continuous casting equipment and an
information processing apparatus.
[0058] FIG. 3 is a view illustrating examples of suitable embedding
positions of temperature sensing units according to the
embodiment.
[0059] FIG. 4 is a characteristic chart illustrating a typical mold
temperature distribution.
[0060] FIG. 5 is a characteristic chart illustrating a temperature
gradient in the typical mold temperature distribution.
[0061] FIG. 6 is a characteristic chart illustrating approximation
accuracy of a mold temperature distribution which is linearly
interpolated according to the embodiment.
[0062] FIG. 7 is a characteristic chart illustrating the mold
temperature distribution which is linearly interpolated according
to the embodiment.
[0063] FIG. 8 is a block diagram illustrating a configuration of
the information processing apparatus functioning as a determination
apparatus of the casting state according to the embodiment.
[0064] FIG. 9 is a characteristic chart illustrating a mold
temperature distribution which is linearly interpolated according
to an example 1.
[0065] FIG. 10 is a characteristic chart illustrating the mold
temperature distribution which is linearly interpolated according
to the example 1.
[0066] FIG. 11 is a characteristic chart illustrating a time change
of short side .beta. differences of heat transfer coefficients
according to an example 2.
[0067] FIG. 12 is a characteristic chart illustrating a time change
of short side s differences of solidified shell thicknesses
according to the example 2.
[0068] FIG. 13 is a characteristic chart illustrating a comparison
of solidified state in mold evaluation amounts according to the
example 2.
[0069] FIG. 14 is a characteristic chart illustrating a comparison
of the solidified state in mold evaluation amounts according to the
example 2.
[0070] FIG. 15 is a characteristic chart illustrating a comparison
of averages of casting state determination amounts which are
classified by layers in the example 2.
[0071] FIG. 16 is a characteristic chart illustrating a comparison
of standard deviations of the casting state determination amounts
which are classified by layers in the example 2.
[0072] FIG. 17 is a characteristic chart illustrating a prediction
value of a ratio where a normal casting is misjudged to be an
abnormal casting relative to an allowable limit value adjustment
constant in the example 2.
[0073] FIG. 18 is a characteristic chart illustrating changes of
the allowable limit values and the casting state determination
amounts where the present invention is applied in the example
2.
[0074] FIG. 19 is a view to explain an outline of the continuous
casting equipment.
[0075] FIG. 20 is a view illustrating a cross section in a vicinity
of a mold of the continuous casting equipment.
DESCRIPTION OF EMBODIMENTS
[0076] Hereinafter, embodiments of the present invention are
described with reference to the attached drawings.
[0077] At first, a partial differential equation to be a
mathematical model which simulates a solidification heat-transfer
phenomenon in a mold in continuous casting and derivation of an
approximate solution by a profile method, and an inverse problem in
which a solidified state in the mold is estimated by using the
approximate solution corresponding to the technology in Patent
Literature 2 are made clear, and the solution is described.
[0078] Next, when an inverse problem method estimating the
solidified state in the mold is applied to an early detection of a
break-out due to drift being an operation failure, a decision
method of concrete allowable limit values of a solidified shell
temperature and a solidified shell thickness to determine an
abnormal casting being a principle part of the present invention is
described.
[0079] FIG. 2 illustrates a part (a right half except an immersion
nozzle) of a cross section in a vicinity of a mold of a continuous
casting equipment. There are a solidified shell 2, a mold flux
layer 3, and a mold 4 being respective thermal conductors between a
molten steel 1 and cooling water 5 for the mold. Thermocouples 6
being a plurality of temperature sensing units are embedded in the
mold 4 in a casting direction, namely, while shifting their
positions downward in the drawing. Besides, an information
processing apparatus 7 functioning as a determination apparatus of
a casting state is equipped.
[0080] [Embedding Positions of Temperature Sensing Units]
[0081] Suitable embedding positions of the temperature sensing
units are described when estimation of the solidified state in the
mold is performed by applying the present invention.
[0082] It is possible to estimate the solidified state in the mold
if the embedding positions of the temperature sensing units are set
under a conventionally used state to monitor the casting state.
However, it is preferable that an arbitrary position within 95 mm
under a supposed molten steel surface level of the mold is set to
P.sub.1, an arbitrary position at 220 mm or more and 400 mm or less
under the molten steel surface level is set to P.sub.2, they are
provided at intervals of 120 mm or less within a range from P.sub.1
to P.sub.2, and at least one point is provided at a position within
300 mm from a lower end of the mold.
[0083] FIG. 3 is a view illustrating examples of the suitable
embedding positions of the temperature sensing units (.cndot. in
FIG. 3) in a mold with a length of 1090 mm where the supposed
molten steel surface level exists at a position of 85 mm from an
upper end of the mold.
[0084] A disposition pattern 1 is a pattern providing at intervals
of 120 mm within a range of 100 mm or more and 340 mm or less from
the upper end of the mold, and providing one point at a position of
250 mm from the lower end of the mold.
[0085] A disposition pattern 2 is a pattern providing at intervals
of 120 mm within a range of 40 mm or more and 400 mm or less from
the upper end of the mold, and providing two points up to the
position of 250 mm from the lower end of the mold.
[0086] A disposition pattern 3 is a pattern providing at intervals
of 60 mm within a range of 100 mm or more and 340 mm or less from
the upper end of the mold, and providing one point at the position
of 250 mm from the lower end of the mold.
[0087] A disposition pattern 4 is a pattern providing at intervals
of 120 mm or less to have irregular intervals within a range of 100
mm or more and 340 mm or less from the upper end of the mold, and
providing one point at the position of 250 mm from the lower end of
the mold.
[0088] Next, reasons why the above-stated embedding positions are
preferable are described. In the present invention, a state in the
mold is estimated by using a temperature distribution of the mold,
and therefore, it is preferable that measurement is performed such
that the temperature distribution of the mold is faithfully
reproduced as much as possible. The measurement is to be performed
by embedding the temperature sensing units in the mold with high
density to enable the faithful reproduction of the mold temperature
distribution, but each temperature sensing unit is an apparatus,
and therefore, it gets out of order at a certain probability. If an
embedding density of the temperature sensing units is made high, a
total failure probability of a plurality of temperature sensing
units increases, and in addition, operation cost increases due to
an expensive construction cost. Accordingly, it is necessary to
perform the measurement properly by embedding the temperature
sensing units in the mold so as to enable the faithful reproduction
of the temperature distribution of the mold by using the
temperature sensing units as little as possible within an allowable
degree.
[0089] In a general continuous casting machine, a molten steel
injection amount is adjusted such that the molten steel surface
level positions at a distance of 80 mm or more and 120 mm or less
from the upper end of the mold for safety reasons such that the
temperature at the upper end of the mold does not become high, the
molten steel does not spill out even when the surface level varies
largely. An inner surface of the mold at an upper side than the
molten steel surface level is therefore exposed to the outside air,
and the upper end part of the mold has a lowest temperature to be
approximately the same temperature as a cooling water temperature
even during the casting. Though the mold temperature changes
depending on casting conditions, the mold temperature increases
from the upper end of the mold toward a vicinity of the molten
steel surface level, a maximum temperature position of the mold
exists from the molten steel surface level to approximately 100 mm
or less under the molten steel surface level, the mold temperature
has a downward trend from the maximum temperature position of the
mold toward the lower end of the mold, and reaches a minimum
temperature of the molten steel surface level or less within 300 mm
from the lower end of the mold.
[0090] FIG. 4 is a typical mold temperature distribution in case
when the molten steel surface level position is 100 mm from the
upper end of the mold in the mold with a length of 900 mm which is
prepared based on a mold temperature measurement result disclosed
in Non-Patent Literature 2. The inventors thought that it was
possible to derive suitable embedding positions of the temperature
sensing units from the typical temperature distribution. Namely,
they thought that a finite number of temperature information was
obtained from the typical temperature distribution, and a
temperature information obtained position where the original
temperature distribution is finely approximated was the suitable
embedding position of the temperature sensing unit when the
temperature distribution is reproduced by a linear
interpolation.
[0091] The temperature sensing units are densely disposed at a
range where a temperature gradient is large or a change of the
temperature gradient is large, and the temperature sensing units
are sparsely disposed at a range where the temperature gradient is
relatively small to faithfully reproduce the temperature
distribution of the mold. When it is considered to estimate the
casting state in the mold by using the temperature distribution
from under the molten steel surface level to a lowermost
temperature sensing unit, it turns out that the temperature sensing
units are densely embedded under the molten steel surface level at
an upper side of the mold, and the temperature sensing units are
coarsely embedded at a lower side of the mold. It is therefore
necessary to decide the temperature sensing position P.sub.2 to be
a boundary between the range to be densely embedded and the range
to be coarsely embedded.
[0092] FIG. 5 is a graphic chart of the temperature gradient of the
typical temperature distribution. There is the boundary between the
range to be densely embedded and the range to be coarsely embedded
at a range from a position of 100 mm under the surface level where
the temperature gradient under the molten steel surface level turns
from positive to negative and the change of the temperature
gradient becomes small compared to the vicinity of the molten steel
surface level to a position of 200 mm from the lower end of the
mold where the temperature reaches the minimum under the molten
steel surface level. The temperature sensing position P.sub.2 to be
the boundary is decided by the following method. Namely, there is
calculated an approximate temperature distribution which is
linearly interpolated by using temperatures of three points at the
position of 100 mm under the molten steel surface level, the
position of 200 mm from the lower end of the mold, and an
intermediate position between the above, a root-mean-square of a
relative difference from the typical temperature distribution is
found, and the intermediate position where the relative difference
becomes small to be within an allowable degree is set to
P.sub.2.
[0093] FIG. 6 is a graphic chart illustrating the root-mean-square
of the relative difference for the intermediate position. When the
intermediate position is 300 mm under the molten steel surface
level, the root-mean square of the relative difference becomes 2.3%
to be a best approximation, and a condition of the temperature
sensing position P.sub.2 is set to suppress the value to 5% or less
being about double of the best approximation. Namely, the
temperature sensing position P.sub.2 is set at 200 mm or more and
400 mm or less from the molten steel surface level.
[0094] FIG. 7 is a graphic chart illustrating the typical
temperature distribution and an approximate temperature
distribution where the temperature sensing position P.sub.2 is set
at 300 mm under the molten steel surface level. It can be seen that
the mold temperature distribution can be accurately and effectively
reproduced by embedding the temperature sensing units within the
above-stated range.
[0095] It is desirable that at least one point is provided at a
position within 300 mm from the lower end of the mold regarding a
disposition at a lower side than the temperature sensing position
P.sub.2, because the temperature reaches the minimum within 300 mm
from the lower end of the mold. A disposition at an upper side than
the temperature sensing position P.sub.2 is decided as follows from
results of the example 1. Namely, the temperature sensing position
P.sub.1 at an uppermost of the range to be densely embedded is set
within 95 mm under the molten steel surface level, and each
interval disposing the temperature sensing unit is set to 120 mm or
less.
[0096] For the reasons as stated above, it is preferable as the
embedding positions of the temperature sensing units that the
arbitrary position within 95 mm from the supposed molten steel
surface level position of the mold is set to P.sub.1, the arbitrary
position at 220 mm or more and 400 mm or less under the molten
steel surface level is set to P.sub.2, the temperature sensing
units are provided at intervals of 120 mm or less within the range
from P.sub.1 to P.sub.2, and at least one point is provided at the
position within 300 mm from the lower end of the mold.
[0097] As stated above, in the general continuous casting machine,
the molten steel injection amount is adjusted such that the
distance of the molten steel surface level from the upper end of
the mold is at a position of 80 mm or more and 120 mm or less.
Accordingly, when P.sub.1 is set at the arbitrary position of 120
mm or more and 175 mm or less from the upper end of the mold, and
P.sub.2 is set at the arbitrary position of 340 mm or more and 480
mm or less from the upper end of the mold, the suitable condition
of the embedding positions of the temperature sensing units is
satisfied regardless of the position of the molten steel surface
level.
[0098] [Estimation Method of Solidified State in Mold]
[0099] The mathematical model used in the present embodiment is
described. In general, there are a plurality of options in the
mathematical models to represent the same phenomenon because
different mathematical models are conceivable by simplifying
components to be factors of the phenomenon. The mathematical model
usable in the present invention is the mathematical model
representing a solidification heat-transfer phenomenon within a
range from the molten metal to the solidified shell 2, the mold
flux layer 3, the mold 4, and the cooling water 5 on a
two-dimensional cross section made up of two directions of a mold
surface vertical direction and a casting direction, as illustrated
in FIG. 2. In addition, a later-described inverse problem is
established within a frame of the mathematical model, and the
inverse problem can be numerically and approximately solved. At
present, there are a partial differential equation where the
expressions (1) to (5) representing the solidification
heat-transfer phenomenon in the mold are simultaneously set up, and
the expressions (6) to (8) representing a heat flux passing through
the mold 4 in different expressions are combined from among the
models satisfying the above-stated conditions which can be executed
on a computer.
[ mathematical expression 1 ] c s .rho. s ( .differential. T
.differential. t + V c .differential. T .differential. z ) =
.lamda. s .differential. 2 T .differential. x 2 x .di-elect cons. (
0 , s ) , z .di-elect cons. ( 0 , z ) , t > 0 ( 1 ) .lamda. s
.differential. T .differential. x = .alpha. ( T - T m ) , x = 0 , z
.di-elect cons. ( 0 , z e ) , t > 0 ( 2 ) .lamda. s
.differential. T .differential. x = .rho. s L ( .differential. s
.differential. t + V c .differential. s .differential. z ) + .beta.
( T 0 - T s ) , z = 0 , t > 0 ( 3 ) T = T s , x = s , z
.di-elect cons. ( 0 , z e ) , t > 0 ( 4 ) s = 0 , z = 0 , t >
0 ( 5 ) [ mathematical expression 2 ] q out = .alpha. ( T | x = 0 -
T m ) , z .di-elect cons. ( 0 , z e ) , t > 0 ( 6 ) q out =
.lamda. m d 1 ( T m - T c ) , z .di-elect cons. ( 0 , z e ) , t
> 0 ( 7 ) q out = 1 1 h w + d 2 .lamda. m ( T c - T w ) , z
.di-elect cons. ( 0 , z e ) , t > 0 ( 8 ) ##EQU00001##
[0100] Here, t is a time. z is a coordinate in the casting
direction when "z=0" is set to the molten steel surface level, x is
a coordinate in the mold vertical direction when "x=0" is set to a
mold surface. z.sub.e is a position of the lowermost thermocouple 6
embedded in the mold 4. C.sub.s is a solidified shell specific
heat, .rho..sub.s is a solidified shell density, is a solidified
shell heat conductivity, and L is a solidification latent heat.
V.sub.c is a casting speed. T.sub.0 is a molten steel temperature,
T.sub.s is a solidification temperature, "T.sub.m=T.sub.m(t, z)" is
a mold surface temperature, "T=T(t, z, x)" is a solidified shell
temperature. "s=s(t, z)" is a solidified shell thickness.
".alpha.=.alpha.(t, z)" is a heat transfer coefficient between the
solidified shell 2 and the mold 4, ".beta.=.beta.(t, z)" is a heat
transfer coefficient between the molten steel 1 and the solidified
shell 2. "q.sub.out=q.sub.out(t, z)" is a heat flux passing through
the mold 4. .lamda..sub.m is a mold heat conductivity. d.sub.1 is a
thermocouple embedded depth from the mold surface, d.sub.2 is a
distance from the thermocouple 6 to the cooling water 5. h.sub.w is
a heat transfer coefficient between the mold and the cooling water.
"T.sub.c=T.sub.c(t, z)" is a mold temperature at a thermocouple
embedded depth position, and "T.sub.w=T.sub.w(t, z)" is a cooling
water temperature.
[0101] This mathematical model is a combination between a model
which simulates a state in the mold where a temperature change
seldom occurs in a horizontal direction in parallel to the mold
surface, and the heat flux in the casting direction in the
solidified shell 2 is extremely small compared to the mold surface
vertical direction and a model which simulates a heat transfer
phenomenon of the mold whose heat conductivity is high. If .alpha.,
.beta., and T.sub.m are given by the later-described profile
method, it is possible to form an approximate solution of the
solidified shell temperature distribution T and the solidified
shell thickness s, and both sufficient accuracy and reduction in a
numerical calculation load to simulate the phenomenon are
satisfied. A real-time calculation solving the later-described
inverse problem is thereby possible owing to this
characteristic.
[0102] Next, derivation of the approximate solution of the
above-stated mathematical model by the profile method is described.
The profile method is a method not solving an objected partial
differential equation in itself but deriving some conditions
satisfied by the solution of the partial differential equation, and
finding the solutions satisfying the conditions by providing
restrictions on the profile. Specifically, the derivation is
performed as described below. At first, the expressions (1) to (5)
are transformed while setting (t.sub.0, .eta.) as a new variable by
a variable transformation from a variable (t, z) by using the
expression (9), then .alpha. is eliminated by using the expression
(6), then the expressions (1) to (5) respectively become the
expressions (10) to (14).
[ mathematical expression 3 ] t = t 0 + .eta. , z = V c .eta. ( 9 )
c s .rho. s .differential. T .differential. .eta. = .lamda. s
.differential. 2 T .differential. x 2 , x .di-elect cons. ( 0 , s )
, .eta. .di-elect cons. ( 0 , z e / V c ) , t 0 > - .eta. ( 10 )
.lamda. s .differential. T .differential. x = q out , x = 0 , .eta.
.di-elect cons. ( 0 , z e / V c ) , t 0 > - .eta. ( 11 ) .lamda.
s .differential. T .differential. x = .rho. s L .differential. s
.differential. .eta. + .beta. ( T 0 - T s ) , x = s , .eta.
.di-elect cons. ( 0 , z e / V c ) , t 0 > - .eta. ( 12 ) T = T s
, x = s , .eta. .di-elect cons. ( 0 , z e / V c ) , t 0 > -
.eta. ( 13 ) s = 0 , .eta. = 0 , t 0 > - .eta. ( 14 )
##EQU00002##
[0103] A differential of t.sub.0 is not appeared in the expressions
(10) to (14), and therefore, hereinafter, t.sub.0 is treated as a
fixed value. Next, a function .psi. used for the profile method is
defined by the expression (15).
[mathematical expression 4]
.PSI.=.rho..sub.s(c.sub.sT.sub.s+L)s-.rho..sub.sc.sub.s.intg..sub.0.sup.-
sTdx, .eta..di-elect cons.[0,z.sub.e/V.sub.c] (15)
[0104] This .psi. is differentiated by .eta., then the expression
(16) representing a balance of the heat flux is obtained by using
the expressions (10) to (13).
[ mathematical expression 5 ] .differential. .PSI. .differential.
.eta. = q out - .beta. ( T 0 - T s ) , .eta. .di-elect cons. ( 0 ,
z e / V c ) ( 16 ) ##EQU00003##
[0105] Actually, it is possible to calculate as the expression
(17), and therefore, both sides of the expression (15) are
differentiated by .eta. and the expression (17) is substituted,
then the expression (16) is obtained.
[ mathematical expression 6 ] .differential. .differential. .eta.
.intg. 0 s Tdx = T | x = s .differential. s .differential. .eta. +
.intg. 0 s .differential. T .differential. .eta. dx = T s
.differential. s .differential. .eta. + .intg. 0 s .lamda. s c s
.rho. s .differential. 2 T .differential. x 2 dx = T s
.differential. s .differential. .eta. + 1 c s .rho. s ( .lamda. s
.differential. T .differential. x | x = s - .lamda. s
.differential. T .differential. x | x = 0 ) = T s .differential. s
.differential. .eta. + 1 c s .rho. s ( .rho. s L .differential. s
.differential. .eta. + .beta. ( T 0 - T s ) - q out ) ( 17 )
##EQU00004##
[0106] Besides, both sides of the expression (13) are
differentiated by .eta., then the expression (18) is obtained.
Besides, if T satisfying both the expression (10) and the
expression (13) exists, the equal sign of the expression (10) holds
true even at the boundary, and if
.differential.T/.differential..eta. and
.differential.s/.differential..eta. are eliminated from the
expression (18) by using the expression (12), the expression (19)
is obtained.
[ mathematical expression 7 ] .differential. T .differential. .eta.
+ .differential. T .differential. x .differential. s .differential.
.eta. = 0 , x = s , .eta. .di-elect cons. ( 0 , z e / V c ) ( 18 )
.lamda. s c s ( .differential. T .differential. x ) 2 - c s .beta.
( T 0 - T s ) .differential. T .differential. x + .lamda. s L
.differential. 2 T .differential. x 2 = 0 , x = s , .eta. .di-elect
cons. ( 0 , z e / V c ) ( 19 ) ##EQU00005##
[0107] As conditions satisfied by the approximate solution by the
profile method, the expressions (20) to (26) are employed by
summarizing the above.
[ mathematical expression 8 ] .PSI. = .rho. s ( c s T s + L ) s -
.rho. s c s .intg. 0 s Tdx , .eta. .di-elect cons. [ 0 , z e / V c
] ( 20 ) .differential. .PSI. .differential. .eta. = q out - .beta.
( T 0 - T s ) , .eta. .di-elect cons. ( 0 , z e / V c ) ( 21 )
.lamda. s .differential. T .differential. x = q out , x = 0 , .eta.
.di-elect cons. ( 0 , z e / V c ) ( 22 ) q out = .alpha. ( T - T m
) , x = 0 , .eta. .di-elect cons. ( 0 , z e / V c ) ( 23 ) .lamda.
s c s ( .differential. T .differential. x ) 2 - c s .beta. ( T 0 -
T s ) .differential. T .differential. x + .lamda. s L
.differential. 2 T .differential. x 2 = 0 , x = s , .eta. .di-elect
cons. ( 0 , z e / V c ) ( 24 ) T = T s , x = s , .eta. .di-elect
cons. ( 0 , z e / V c ) ( 25 ) s = 0 , .eta. = 0 ( 26 )
##EQU00006##
[0108] The profile of T is made quadratic relative to x, and T is
given by the expression (27) so as to constantly satisfy the
expression (25).
[mathematical expression 9]
T=T.sub.s+a(x-s)+b(x-s).sup.2, x.di-elect cons.[0,s],
.eta..di-elect cons.[0,z.sub.e/V.sub.c] (27)
[0109] Here, a=a(.eta.) and b=b(.eta.) are independent from x, and
it is possible to concretely find by substituting the expression
(27) into the expressions (22) and (24). Actually, the expression
(28) holds true when the expression (27) is differentiated by x,
and the expression (22) and the expressions (24) to (29) are
obtained, and therefore, the expression (30) and the expression
(31) are obtained under a condition of
.differential.T/.differential..times.|.sub.x=s>0 representing
that the heat flux goes from the molten steel side to the
solidified shell.
[ mathematical expression 10 ] .differential. T .differential. x =
a + 2 b ( x - s ) , .differential. 2 T .differential. x 2 = 2 b , (
28 ) .lamda. s ( a - 2 b - s ) = q out , .lamda. s c s a 2 - c s
.beta. ( T 0 - T s ) a + 2 L .lamda. s b = 0 ( 29 ) a = 1 2 .lamda.
s c s ( c s .beta. ( T 0 - T s ) - L .lamda. s s + { c s .beta. ( T
0 - T s ) - L .lamda. s s } 2 + 4 L q out .lamda. s c s s ) ( 30 )
b = 1 2 s ( a - q out .lamda. s ) ( 31 ) ##EQU00007##
[0110] Besides, the expression (27) is integrated relative to x to
be the expression (32), and therefore, the expression (33) is
obtained by substituting the expression (32), the expression (31),
and the expression (30) into the expression (20).
[ mathematical expression 11 ] .intg. 0 s Tdx = T s s - a 2 s 2 + b
3 s 3 ( 32 ) .PSI. = 5 6 L .rho. s s + c s .rho. s s 2 6 .lamda. s
( q out + .beta. ( T 0 - T s ) ) + .rho. s s 6 .lamda. s ( c s
.beta. ( T 0 - T s ) s - L .lamda. s ) 2 + 4 L q out .lamda. s c s
s ( 33 ) ##EQU00008##
[0111] On the other hand, when x="0" (zero), the expression (31)
and the expression (30) are substituted into the expression (27),
the expression (34) is obtained.
[ mathematical expression 12 ] T | x = 0 = T s - q out s 2 .lamda.
s - c s .beta. ( T 0 - T s ) s - L .lamda. s 4 .lamda. s c s - 1 4
.lamda. s c s { c s .beta. ( T 0 - T s ) s - L .lamda. s } 2 + 4 L
q out .lamda. s c s s ( 34 ) ##EQU00009##
[0112] The expression (23) is substituted into the expression (34),
then it is simplified by T|.sub.x=0-T.sub.m to obtain the
expression (35).
[mathematical expression 13]
A.sub.2(T|.sub.x=0-T.sub.m).sup.2+A.sub.1(T|.sub.x=0-T.sub.m)+A.sub.0=0
(35)
[0113] Note that A.sub.2, A.sub.1, and A.sub.0 are respectively
given by the expression (36), the expression (37), and the
expression (38).
[ mathematical expression 14 ] A 2 = ( 1 + .alpha. s 2 .lamda. s )
2 ( 36 ) A 1 = 2 ( 1 + .alpha. s 2 .lamda. s ) ( c s .beta. ( T 0 -
T s ) s - L .lamda. s 4 .lamda. s c s - T s + T m ) - L s .alpha. 4
.lamda. s c s ( 37 ) A 0 = ( c s .beta. ( T 0 - T s ) s - L .lamda.
s 4 .lamda. s c s - T s + T m ) 2 - ( c s .beta. ( T 0 - T s ) s -
L .lamda. s 4 .lamda. s c s ) 2 ( 38 ) ##EQU00010##
[0114] When s=0 in the expression (34), then T|.sub.x=0=T.sub.s is
considered, T|.sub.x=0 given by the expression (39) simultaneously
satisfies the expression (34) and the expression (23) between two
solutions of the expression (35) relating to T|.sub.x=0.
[ mathematical expression 15 ] T | x = 0 = T m + 1 2 A 2 ( - A 1 -
A 1 2 - 4 A 2 A 0 ) ( 39 ) ##EQU00011##
[0115] In summary, the approximate solution by the profile method
satisfies the expressions (40) to (44).
[ mathematical expression 16 ] s = 0 , .eta. = 0 ( 40 ) T | x = 0 =
T m + 1 2 A 2 ( - A 1 - A 1 2 - 4 A 2 A 0 ) , .eta. .di-elect cons.
( 0 , z e / V c ) ( 41 ) q out = .alpha. ( T | x = 0 - T m ) ,
.eta. .di-elect cons. ( 0 , z e / V c ) ( 42 ) .differential. .PSI.
.differential. .eta. = q out - .beta. ( T 0 - T s ) , .eta.
.di-elect cons. ( 0 , z e / V c ) ( 43 ) .PSI. = 5 6 L .rho. s s +
c s .rho. s s 2 6 .lamda. s ( q out + .beta. ( T 0 - T s ) ) +
.rho. s s 6 .lamda. s ( c s .beta. ( T 0 - T s ) s - L .lamda. s )
2 + 4 L q out .lamda. s c s s , .eta. .di-elect cons. [ 0 , z e / V
c ] ( 44 ) ##EQU00012##
[0116] Note that A.sub.2, A.sub.1, and A.sub.0 in the expression
(41) are respectively given by the expressions (36) to (38).
Processes until the derivation of the expressions (40) to (44) are
an equation construction step. Besides, if it is possible to
construct s satisfying the expressions (40) to (44), q.sub.out can
be found from the expression (42), then T is defined by the
expression (27) from the expressions (30) and (31), and it turns
out that the expressions (20) to (26) are satisfied. Accordingly,
if s satisfying the expressions (40) to (44) can be found, the
approximate solution by the profile method is constructed, but this
can be numerically obtained by differentiating the expression (43).
Specifically, it goes as stated below. Setting c.sub.s,
.rho..sub.s, .lamda..sub.s, L, T.sub.0, T.sub.s as known constants,
and regarding .eta., calculation points are set to .eta..sub.0=0,
.eta..sub.i=.eta..sub.i-1+d.eta. (d.eta.>0, i=1, 2, . . . , n),
.eta..sub.n=z.sub.e/V.sub.c. When .alpha., .beta., and T.sub.m are
given by .eta.=.eta..sub.i, they are respectively set to
.alpha..sub.i, .beta..sub.i, and T.sub.m, i. The expression (43) is
differentiated by Euler method, and an approximate value of
.psi.(.eta..sub.i) is represented by .psi..sub.i, it becomes as
represented by the expression (45).
[mathematical expression 17]
.PSI..sub.i=1=.PSI..sub.i+d.eta.{q.sub.out-.beta..sub.i(T.sub.0-T.sub.s)-
}, i=0,1, . . . ,n-1 (45)
[0117] Then, an approximate value s.sub.i of s(.eta..sub.i) can be
recursively calculated as illustrated below. At first, s.sub.0=0
from the expression (40), and .psi..sub.0=0 from the expression
(44). Next, when s.sub.i and .psi..sub.i are given, .alpha..sub.i,
.beta..sub.i, and T.sub.m, i, and s.sub.i are respectively
substituted into .alpha., .beta., T.sub.m, and s in the expressions
(36) to (38). Then, T|.sub.x=0 is found from the expression (41),
q.sub.out is found from the expression (42), and .psi..sub.i+1 is
found from the expression (45). Next, .psi..sub.i+1 and
.beta..sub.i+1 are substituted into .psi. and .beta. in the
expression (44), q.sub.out obtained by the expression (42) is
substituted into q.sub.out to solve as for s to be s.sub.i+1. It is
thereby possible to find s.sub.i+1 and .psi..sub.i+1 from s.sub.i
and .psi..sub.i, so it is possible to recursively define
s.sub.i.
[0118] Hereinabove, it is described that T and s are able to be
found by using the profile method while setting t.sub.0 as an
arbitrary time, on t=t.sub.0+.eta., z=V.sub.c.eta. for
.eta..di-elect cons.[0, z.sub.e/V.sub.c] when c.sub.s, .rho..sub.s,
.lamda..sub.s, L, T.sub.0, T.sub.s V.sub.0 are already known, and
.alpha., .beta., T.sub.m are given. Hereinafter, T and s obtained
by the above-stated profile method are represented by the
expression (46) because T and s depend on .alpha., .beta., and
T.sub.m.
[mathematical expression 18]
T.sub.prof(.alpha.,.beta.,T.sub.m) and
s.sub.prof(.alpha.,.beta.,T.sub.m) (46)
[0119] Next, formulation as an inverse problem and a solution
thereof are described. The inverse problem is a generic of a
problem estimating a cause from a result. Within a frame of the
mathematical model representing the solidification heat-transfer
phenomenon in the mold, it is possible to immediately calculate the
expression (47) and the expression (48) being the mold surface
temperature and the heat flux passing through the mold from the
expression (7) and the expression (8) when .lamda..sub.m, d.sub.1,
d.sub.2, h.sub.w, c.sub.s, .rho..sub.s, .lamda..sub.s, L, T.sub.0,
T.sub.s, T.sub.w, and V.sub.c are set to be already known, and
t.sub.0=t.sub.1-z.sub.1/V.sub.c at (t.sub.1, z.sub.1) where
t.sub.1-z.sub.i/V.sub.c is during the casting time for
z.sub.1.di-elect cons.(0, z.sub.e), and when T.sub.c where the
measurement values by the thermocouples 6 embedded in the mold 4
for .eta..di-elect cons.(0, z.sub.i/V.sub.c) are interpolated on
t=t.sub.0+.eta., z=V.sub.c.eta. is obtained.
[ mathematical expression 19 ] T m = T c + d 1 .lamda. m 1 1 h w +
d 2 .lamda. m ( T c - T w ) , .eta. .di-elect cons. ( 0 , z 1 / V c
) ( 40 ) q out = 1 1 h w + d 2 .lamda. m ( T c - T w ) , .eta.
.di-elect cons. ( 0 , z 1 / V c ) ( 41 ) ##EQU00013##
[0120] On the other hand, the heat flux passing through the mold
flux layer 3 is represented by the expression (49) from the
expression (6) and the expression (7).
[ mathematical expression 20 ] q out = 1 1 .alpha. + d 1 .lamda. m
( T prof ( .alpha. , .beta. , T m ) | x = 0 - T c ) , .eta.
.di-elect cons. ( 0 , z 1 / V c ) ( 49 ) ##EQU00014##
[0121] Accordingly, a problem estimating .alpha. and .beta. such
that the expression (49) holds true for q.sub.out given by the
expression (48) is the inverse problem in the solidification
heat-transfer phenomenon in the mold. This inverse problem is
resolved to solve a minimization problem by a least squares method
represented by the expression (50) for q.sub.out given by the
expression (48).
[ mathematical expression 21 ] min .alpha. = ( .alpha. 0 , ,
.alpha. n ) , .beta. = ( .beta. 0 , , .beta. n ) , .alpha. i > 0
, .beta. i > 0 i = 1 n q out | .eta. = .eta. i - 1 1 .alpha. i +
d 1 .lamda. m ( T prof ( .alpha. , .beta. , T m ) | x = 0 - T c ) |
.eta. = .eta. i 2 ( 50 ) ##EQU00015##
[0122] Here, .eta..sub.0=0,
.eta..sub.i=.eta..sub.i-1+d.eta.(d.eta.>0, i=1, 2, . . . , n),
.eta..sub.n=z.sub.i/V.sub.c, and as stated above, it is possible to
numerically calculate T.sub.prof(.alpha., .beta., and T.sub.m),
therefore, the minimization problem is able to be solved by a
general numerical solution using a Gauss-Newton method or the like.
It is a heat transfer coefficient estimation step to solve the
minimization problem of the expression (50), and the solidified
shell thickness, and the solidified shell temperature are obtained
by substituting .alpha., .beta., and T.sub.m decided at each time,
each position (t, z) into the expression (46). It is therefore
possible to obtain the heat transfer coefficient .alpha., the heat
transfer coefficient .beta., the solidified shell thickness s, and
the solidified shell temperature T being the solidified state in
mold estimation amounts at (t, z). These solidified state in mold
estimation amounts are hereinafter respectively represented as
.alpha..sub.est(t, z), .beta..sub.est(t, z), s.sub.est(t, z), and
T.sub.est(t, z, x).
[0123] Hereinabove is the estimation method of the state in the
mold described in Patent Literature 2.
[0124] [Decision Method of Allowable Limit Values]
[0125] Next, a decision method of concrete allowable limit values
to determine signs of the abnormal casting is described before the
inverse problem method estimating the state in the mold is applied
to an early detection method of the break-out due to drift being
the abnormal casting.
[0126] At first, the mold temperatures or the like during casting
are stored in advance. At that time, the casting speed, a
super-heat being a difference between a molten steel temperature
and a solidification temperature, a casting width being casting
conditions are also stored as time-series data. The continuous
casting equipment where the present invention can be applied is a
continuous casting equipment where the abnormal casting has
occurred, and temperature information or the like measured when the
abnormal casting occurred has been stored.
[0127] Next, calculation expressions to be the solidified state in
mold evaluation amounts are prepared. Ones which can be the
solidified state in mold evaluation amounts are ones using the
solidified state in mold estimation amounts which change caused by
drifting of the flow of the molten steel, and it becomes "0" (zero)
if the drift does not occur, and becomes a positive or negative
value in accordance with a direction and a size of the drift when
the drift occurs. For example, evaluation values defined by the
following expression (51), expression (52), expression (53), or
expression (54) become the solidified state in mold evaluation
amounts.
[ mathematical expression 22 ] mean t - ( m - 1 ) .delta. t
.ltoreq. .tau. .ltoreq. t ( s est L - s est R ) ( .tau. , z ) = 1 m
j = 1 m ( s est L ( t - ( j - 1 ) .delta. t , z ) - s est R ( t - (
j - 1 ) .delta. t , z ) ) ( 51 ) mean t - ( m - 1 ) .delta. t
.ltoreq. .tau. .ltoreq. t ( .beta. est L - .beta. est R ) ( .tau. ,
z ) = 1 m j = 1 m ( .beta. est L ( t - ( j - 1 ) .delta. t , z ) -
.beta. est R ( t - ( j - 1 ) .delta. t , z ) ) ( 52 ) sgn min t - (
m - 1 ) .delta. t .ltoreq. .tau. .ltoreq. t ( s est L - s est R ) (
.tau. , z ) = sgn ( mean t - ( m - 1 ) .delta. t .ltoreq. .tau.
.ltoreq. t ( s est L - s est R ) ( .tau. , z ) ) min t - ( m - 1 )
.delta. t .ltoreq. .tau. .ltoreq. t ( s est L - s est R ) ( .tau. ,
z ) ( 53 ) sgnmin t - ( m - 1 ) .delta. t .ltoreq. .tau. .ltoreq. t
( .beta. est L - .beta. est R ) ( .tau. , z ) = sgn ( mean t - ( m
- 1 ) .delta. t .ltoreq. .tau. .ltoreq. t ( .beta. est L - .beta.
est R ) ( .tau. , z ) ) min t - ( m - 1 ) .delta. t .ltoreq. .tau.
.ltoreq. t ( .beta. est L - .beta. est R ) ( .tau. , z ) ( 54 )
##EQU00016##
[0128] Here, s.sub.estL(t, z), s.sub.estR(t, z), .beta..sub.estL(t,
z), and .beta..sub.estR(t, z) respectively represent the solidified
shell estimated thicknesses and the heat transfer coefficients
.beta. being the solidified state in mold estimation amounts at
short sides of two planes by using subscripts L, R distinguishing
right and left short sides. Besides, .delta.t is a sampling cycle,
m.delta.t is an evaluation time, and sgn is a sign of a number. The
expression (51) and the expression (52) are moving average values
of past m.delta.t, and the expression (53) and the expression (54)
are ones where a minimum value of the past m.delta.t regarding an
absolute value of a difference of state quantities is multiplied by
a sign representing the direction of the drift. There are
flexibilities in an evaluation time m and an evaluation position z
in the solidified state in mold evaluation amounts, and therefore,
one solidified state in mold evaluation amount is obtained every
time when one combination of m and z is specified. In the
solidified state in mold evaluation amounts as stated above, it is
necessary to discretely select a plurality of representative m and
z to select a best casting state determination amount for an
objected continuous casting equipment.
[0129] Next, an allowable limit value examination period is
provided in advance, the solidified state in mold estimation
amounts are found from the measurement data during the allowable
limit value examination period, and candidates of the solidified
state in mold evaluation amounts are also calculated and stored.
The casting conditions are classified by layers while defining a
grade width regarded to be the same, and respective layers are
represented by G.sub.1, . . . G.sub.N. The solidified state in mold
evaluation amounts are also classified by layers in accordance with
G.sub.k, and an average value .mu..sub.k and a standard deviation
.sigma..sub.k are calculated by each of the solidified state in
mold evaluation amounts classified by layers. Here, k=1, N each
represent a subscript of each classified layer, and N is a total
number of layers. It is desirable that the allowable limit value
examination period is set to be long enough such that a statistic
calculated from the casting condition G.sub.k classified by layers
can be estimated with allowable accuracy. Besides, the solidified
state in mold estimation amounts and the solidified state in mold
evaluation amounts are classified by layers in accordance with
classifications for the casting conditions and the measurement
values set in advance. The casting conditions and the measurement
values are one or more kinds from among the casting speed, the
casting width, the molten steel temperature, the difference between
the molten steel temperature and the liquidus temperature, and the
difference between the molten steel temperature and the solidus
temperature.
[0130] Next, the solidified state in mold estimation amounts are
found by solving the inverse problem from the measurement data of
the break-out due to drift being the abnormal casting occurred in
the past, the solidified state in mold evaluation amounts are
calculated, and one whose solidified state in mold evaluation
amount just before the break-out occurrence is the most separated
from a normal time is selected as a casting state determination
amount. A value of the solidified state in mold evaluation amount
just before the occurrence of the break-out due to drift being the
abnormal casting is represented by E, then the casting state
determination amount is set by selecting the solidified state in
mold evaluation amount where a value given by the expression (55)
becomes a maximum relative to .mu..sub.k and .sigma..sub.k of the
solidified state in mold evaluation amounts of the layer where the
casting condition at the break-out occurrence time belongs.
[mathematical expression 23]
|E-.mu..sub.k|/.sigma..sub.k (55)
[0131] Which solidified state in mold evaluation amount is able to
sense the drift with high sensitivity depends on the continuous
casting equipment, and therefore, it is necessary to select the
solidified state in mold evaluation amount in accordance with a
casting machine. A positive constant to adjust the allowable limit
value for the selected casting state determination amount is
represented by A, a total sum of time satisfying the expression
(56) under each casting condition G.sub.k is calculated, and a
ratio for the allowable limit value examination period is
found.
[mathematical expression 24]
|casting state determination amount-.mu..sub.k|>A.sigma..sub.k
(56)
[0132] This ratio corresponds to a ratio where the normal casting
is misjudged to be the casting where the break-out due to drift
occurs, and the ratio decreases if A is set large. It is thereby
possible to detect the casting failure leading to the break-out due
to drift being the abnormal casting with high accuracy as long as
the positive constant A where the above-stated ratio is allowable,
and the expression (56) is satisfied in the past abnormal casting
is selected. It is a decision method of the allowable limit values
to set the allowable limit values associated with each casting
condition G.sub.k at .mu..sub.k.+-.A.sigma..sub.k for the selected
A. Namely, a value where one time or more value of the standard
deviation .sigma..sub.k is added to the average value .mu..sub.k
and a value where one time or more value of the standard deviation
.sigma..sub.k is subtracted from the average value .mu..sub.k are
used as the allowable limit values.
[0133] When the allowable limit values are actually applied, the
average value .mu..sub.k and the standard deviation .sigma..sub.k
of the solidified state in mold evaluation amounts corresponding to
G.sub.k where the current casting conditions belong are taken out,
then it is determined as a normal casting state when the casting
state determination amount found by actual measurement satisfies
the expression (57), and it is determined as an abnormal casting
state where there is a high risk of the occurrence of the break-out
due to drift if the expression (57) is not satisfied. This is the
determination method of the casting state.
[mathematical expression 25]
.mu..sub.k-A.sigma..sub.k<casting state determination
amount<.mu..sub.k+A.sigma..sub.k (57)
[0134] Hereinafter, the determination method of the casting state
according to the present embodiment is described by using a
flowchart illustrated in FIG. 1.
[0135] At first, the mold heat conductivity .lamda..sub.m, the
thermocouple embedded depth from the mold surface d.sub.1, the
distance from the thermocouple 6 to the cooling water 5 d.sub.2,
the heat transfer coefficient between the mold and the cooling
water h.sub.w, the solidified shell specific heat c.sub.s, the
solidified shell density .rho..sub.s, the solidified shell heat
conductivity .lamda..sub.s, the solidification latent heat L, and
the solidified temperature T.sub.s each of which are able to be
known in advance are set to be already known regarding a size and
physical property values of the mold 4, and physical property
values of the molten steel 1 to be a casting object when the
casting is performed. As for the molten steel temperature T.sub.0,
the cooling water temperature T.sub.w, and the casting speed
V.sub.c which may change during casting, it is possible to set them
to be already known by using average values, but it is desirable to
measure them in step S101 as same as the mold temperature
T.sub.c.
[0136] In a mold temperature measurement step of the step S101, the
mold temperature T.sub.c at the thermocouple embedded depth
position is found by measuring and interpolating the mold
temperature, the temperature distribution in the casting direction
is found, and they are stored in a data storage part in
time-series.
[0137] In a heat flux obtaining step of step S102, the heat flux
q.sub.out passing through the mold 4 is found from the mold
temperature T.sub.c obtained in the step S101 by using the
expression (48).
[0138] In a mold surface temperature obtaining step of step S103,
the mold surface temperature T.sub.m is found from the mold
temperature T.sub.c obtained in the step S101 by using the
expression (47).
[0139] In an equation construction step of step S104, the partial
differential equation being a partial differential equation which
contains at least the heat transfer coefficient .alpha., the heat
transfer coefficient .beta., the solidified shell thickness s, and
the solidified shell temperature T represented by the expressions
(40) to (44), and regarding a time representing a balance of the
heat flux at the solidified shell 2 is constructed as a preparation
for a causal relation expression construction step of step
S105.
[0140] In the causal relation expression construction step of the
step S105, the partial differential equation constructed in the
step S104 is solved, then there are constructed: a solidified shell
temperature expression being a relational expression of the
solidified shell temperature relative to the heat transfer
coefficient .alpha., the heat transfer coefficient .beta., and the
mold surface temperature which are represented by the expression
(46) and the expression (49); a solidified shell thickness
expression being a relational expression of the solidified shell
thickness relative to the heat transfer coefficient .alpha., the
heat transfer coefficient .beta., and the mold surface temperature;
and a mold flux layer heat flux expression being a relational
expression of the mold flux layer heat flux relative to the heat
transfer coefficient .alpha., the heat transfer coefficient .beta.,
and the mold surface temperature as the causal relation expression,
as a preparation for a heat transfer coefficient estimation step of
step S106.
[0141] In the heat transfer coefficient estimation step of the step
S106, the mold surface temperature T.sub.m obtained in the step
S103 is applied to the mold flux layer heat flux expression
obtained in the step S105, the minimization problem of the
expression (50) being the inverse problem simultaneously deciding a
distribution of the heat transfer coefficient .alpha. in the
casting direction and a distribution of the heat transfer
coefficient .beta. in the casting direction is solved such that a
total sum of values at a plurality of points becomes the minimum
regarding a distribution in the casting direction of a square value
where the mold heat flux q.sub.out obtained in the step S102 is
subtracted from the mold flux layer heat flux expression, to
thereby simultaneously decide the heat transfer coefficient .alpha.
and the heat transfer coefficient .beta..
[0142] In a solidified shell estimation step of step S107, the
solidified shell estimated temperature and the solidified shell
estimated thickness are decided by applying the mold surface
temperature T.sub.m obtained in the step S103, the heat transfer
coefficient .alpha. and the heat transfer coefficient .beta.
obtained in the step S106 to the solidified shell temperature
expression and the solidified shell thickness expression obtained
in the step S105, namely, T.sub.prof(.alpha., .beta., T.sub.m) and
s.sub.prof(.alpha., .beta., T.sub.m) in the expression (46).
[0143] In a solidified state in mold evaluation step of step S108,
the solidified state in mold evaluation amounts are calculated in
response to a calculation method defined in advance from the heat
transfer coefficient .alpha. and the heat transfer coefficient
.beta. obtained in the step S106 and the solidified shell estimated
temperature and the solidified shell estimated thickness obtained
in the step S107. Namely, the heat transfer coefficient .alpha.,
the heat transfer coefficient .beta. obtained in the step S106 and
the solidified shell estimated thickness, the solidified shell
estimated temperature obtained in the step S107 are called as the
solidified state in mold estimation amounts, and there are decided
the solidified state in mold evaluation amounts being the amounts
obtained by applying the calculation method defined in advance to
at least one or a plurality of the solidified state in mold
estimation amounts.
[0144] In an allowable limit value presence/absence determination
step of step S109, it is determined whether or not the allowable
limit values found in an allowable limit value storing step of step
S113 are stored in a data storage part. When the allowable limit
values are not stored, the process goes to a time-series data
storing step of step S110 being a preparation step to find the
allowable limit values, and when the allowable limit values are
stored, the process goes to step S114 to determine the casting
state.
[0145] In the time-series data storing step of the step S110, at
least one or more kinds of amounts contained in the solidified
state in mold estimation amounts and the solidified state in mold
evaluation amounts defined in the step S108 are stored in the data
storage part as a time-series data together with information
indicating whether or not the abnormal casting occurred to
calculate a statistic.
[0146] In a statistic calculation determination step of step S111,
it is determined whether or not the time-series data stored in the
step S110 are accumulated for a period defined in advance, and it
is possible to calculate the statistic including the average and
the standard deviation of the time-series data. If the statistic of
the time-series data cannot be calculated, the process returns to
the mold temperature measurement step of the step S101 to increase
the number of data, and the measurement is newly performed again.
If the statistic of the time-series data can be calculated, the
process goes to an operation failure time data presence/absence
determination step of step S112.
[0147] In the operation failure time data presence/absence
determination step of the step S112, it is determined whether or
not at least one or more kinds of amounts contained in the
solidified state in mold estimation amounts and the solidified
state in mold evaluation amounts when the abnormal casting occurred
are stored in the data storage part. If they are stored, the
process goes to the allowable limit value storing step of the step
S113 being the step to define the allowable limit values, and if
they are not stored, the process returns to the mold temperature
measurement step of the step S101, and the measurement is newly
performed again.
[0148] In the allowable limit value storing step of the step S113,
the casting state determination amount being an amount used for the
determination of the casting state is selected from the stored
time-series data by using the time-series data when the abnormal
casting occurred, and the statistic information including the
average and the standard deviation of the time-series data obtained
in the step S110, the allowable limit values defining a range of
data regarded to be the normal casting state are decided as for the
casting state determination amount, and stores the allowable limit
values in the data storage part. After the allowable limit values
are decided and stored in the data storage part, the process
returns to the mold temperature measurement step of the step S101,
and the measurement is newly performed again.
[0149] On the other hand, in a casting state determination step of
the step S114, the allowable limit values are compared with the
amount which is selected as the casting state determination amount
in the step S113 from among the solidified state in mold estimation
amounts obtained in the steps S106, S107 and the solidified state
in mold evaluation amounts obtained in the step S108. If it is
determined to be the normal casting state, the process returns to
the mold temperature measurement step of the step S101, and the
measurement is newly performed again. If it is determined to be the
abnormal casting state, the process goes to step S115.
[0150] In the step S115, an operation action such that, for
example, the casting speed is lowered is performed so as to prevent
the operation failure resulting from the abnormal casting state.
The operation actions to be performed are set in advance.
[0151] As stated above, the heat transfer coefficient .alpha. being
the heat flux per a unit temperature difference between the
solidified shell 2 and the mold 4 sandwiching the mold flux layer
3, and the heat transfer coefficient .beta. between the molten
steel 1 and the solidified shell 2 are found by solving the inverse
problem, the solidified shell thickness s and the solidified shell
temperature T distribution of the solidified shell 2 are estimated
from the heat transfer coefficient .alpha. and the heat transfer
coefficient .beta., and it is determined whether the normal casting
state or the abnormal casting state by using the estimated
results.
[0152] A configuration of the information processing apparatus 7
functioning as a determination apparatus of the casting state is
illustrated in FIG. 8.
[0153] The temperature measurement results of the mold 4 by using
the thermocouples 6 during the continuous casting are input to the
information processing apparatus 7, the temperature distribution in
the casting direction at the thermocouple embedded depth positions
which is obtained by interpolating the mold temperatures is stored
in a data storage part 313 in time series, and the data is
transmitted to a heat flux obtaining part 301.
[0154] At the heat flux obtaining part 301, the heat flux q.sub.out
passing through the mold 4 is found from the mold temperature
T.sub.c by using the expression (48).
[0155] At a mold surface temperature obtaining part 302, the mold
surface temperature T.sub.m is found from the mold temperature
T.sub.c by using the expression (47).
[0156] At an equation construction part 303, a partial differential
equation being a partial differential equation which contains at
least the heat transfer coefficient .alpha., the heat transfer
coefficient .beta., the solidified shell thickness s, and the
solidified shell temperature T represented by the expressions (40)
to (44), and regarding the time representing the balance of the
heat flux at the solidified shell 2 is constructed as a preparation
for a process by a causal relation expression construction part
304.
[0157] At the causal relation expression construction part 304, the
partial differential equation constructed at the equation
construction part 303 is solved, then there are constructed: the
solidified shell temperature expression being the relational
expression of the solidified shell temperature relative to the heat
transfer coefficient .alpha., the heat transfer coefficient .beta.,
and the mold surface temperature represented by the expression (46)
and the expression (49); the solidified shell thickness expression
being the relational expression of the solidified shell thickness
relative to the heat transfer coefficient .alpha., the heat
transfer coefficient .beta., and the mold surface temperature; and
the mold flux layer heat flux expression being the relational
expression of the mold flux layer heat flux relative to the heat
transfer coefficient .alpha., the heat transfer coefficient .beta.,
and the mold surface temperature as the causal relation expression
as a preparation for a process by a heat transfer coefficient
estimation part 305.
[0158] At the heat transfer coefficient estimation part 305, the
heat transfer coefficient .alpha. and the heat transfer coefficient
.beta. are simultaneously decided by applying the mold surface
temperature T.sub.m obtained by the mold surface temperature
obtaining part 302 to the mold flux layer heat flux expression
obtained at the causal relation expression construction part 304,
and solving the minimization problem of the expression (50) being
the inverse problem simultaneously deciding the distribution of the
heat transfer coefficient .alpha. in the casting direction and the
distribution of the heat transfer coefficient .beta. in the casting
direction such that the total sum of the values at the plurality of
points becomes the minimum regarding the distribution in the
casting direction of the square value of the value where the mold
heat flux q.sub.out obtained at the heat flux obtaining part 301 is
subtracted from the mold flux layer heat flux expression.
[0159] At a solidified shell estimation part 306, the solidified
shell estimated temperature and the solidified shell estimated
thickness are decided by applying the mold surface temperature
T.sub.m obtained at the mold surface temperature obtaining part
302, the heat transfer coefficient .alpha. and the heat transfer
coefficient .beta. obtained at the heat transfer coefficient
estimation part 305 to the solidified shell temperature expression
and the solidified shell thickness expression obtained at the
causal relation expression construction part 304, namely
T.sub.prof(.alpha., .beta., T.sub.m) and s.sub.prof(.alpha.,
.beta., T.sub.m) in the expression (46).
[0160] At a solidified state in mold evaluation part 307, the
solidified state in mold evaluation amounts are calculated in
response to the calculation method defined in advance from the heat
transfer coefficient .alpha. and the heat transfer coefficient
.beta. obtained at the heat transfer coefficient estimation part
305, the solidified shell estimated temperature and the solidified
shell estimated thickness obtained at the solidified shell
estimation part 306. Namely, the heat transfer coefficient .alpha.
and the heat transfer coefficient .beta. obtained at the heat
transfer coefficient estimation part 305, the solidified shell
estimated temperature and the solidified shell estimated thickness
obtained at the solidified shell estimation part 306 are called as
the solidified state in mold estimation amounts, and the solidified
state in mold evaluation amounts being the amounts obtained by
applying the calculation method defined in advance to at least one
or a plurality of the solidified state in mold estimation amounts
are decided.
[0161] At an allowable limit value presence/absence determination
part 308, it is determined whether or not the allowable limit
values found at an allowable limit value storage part 312 are
stored in the data storage part 313. If the allowable limit values
are not stored, the process is performed by a time-series data
storage part 309 as a preparation to find the allowable limit
values, and if the allowable limit values are stored, the process
is performed by a casting state determination part 314.
[0162] At the time-series data storage part 309, at least one or
more kinds of amounts contained in the solidified state in mold
estimation amounts and the solidified state in mold evaluation
amounts defined at the solidified state in mold evaluation part 307
are stored as the time-series data in the data storage part 313
together with the information whether or not the abnormal casting
occurred to calculate the statistic.
[0163] At a statistic calculation determination part 310, it is
determined whether or not the time-series data stored at the
time-series data storage part 309 are accumulated for the period
defined in advance, and the statistic including the average and the
standard deviation of the time-series data can be calculated. If
the statistic of the time-series data cannot be calculated, the
mold temperature is newly measured again to increase the number of
data. If the statistic of the time-series data can be calculated,
the process is performed by an operation failure time data
presence/absence determination part 311.
[0164] At the operation failure time data presence/absence
determination part 311, it is determined whether or not at least
one or more kinds of amounts contained in the solidified state in
mold estimation amounts and the solidified state in mold evaluation
amounts when the abnormal casting occurred are stored in the data
storage part 313. If they are stored, the process is performed by
the allowable limit value storage part 312 which defines the
allowable limit values, and if they are not stored, the mold
temperature is newly measured again.
[0165] At the allowable limit value storage part 312, the casting
state determination amount being the amount used for the
determination of the casting state is selected from the data stored
as the time-series data by using the time-series data when
abnormality occurred in the casting state, the statistic
information including the average and the standard deviation of the
time-series data obtained at the time-series data storage part 309,
the allowable limit values defining a data range regarded as the
normal casting state are decided as for the casting state
determination amount, and they are stored in the data storage part
313. After the allowable limit values are decided and stored in the
data storage part 313, the mold temperature is newly measured
again.
[0166] At a casting state determination part 314, the allowable
limit values are compared with the amount selected as the casting
state determination amount at the allowable limit value storage
part 312 from among the solidified state in mold estimation amounts
obtained at the heat transfer coefficient estimation part 305 and
the solidified shell estimation part 306, and the solidified state
in mold evaluation amounts obtained at the solidified state in mold
evaluation part 307. If it is determined as the normal casting
state, the mold temperature is newly measured again. Then the
result determining either the normal casting state or the abnormal
casting state is output from an output part 315.
[0167] Note that the present invention is able to be enabled by a
computer executing a program. Besides, a computer readable
recording medium recording this program and a computer program
product such as the program are also applied as the present
invention. As the recording medium, it is possible to use, for
example, a flexible disk, a hard disk, an optical disk, a
magneto-optical disk, a CD-ROM, a magnetic tape, a non-volatile
memory card, a ROM, and so on.
[0168] Further, the above-described embodiment merely illustrates,
in its entirety, an example of implementing the present invention,
and therefore the technical scope of the present invention should
not be construed in any restrictive sense by the embodiment. That
is, the invention may be embodied in various forms without
departing from the spirit or essential characteristics thereof.
EXAMPLES
[0169] Next, examples where the present invention is applied are
described.
Example 1
[0170] The present example evaluates influence of the embedding
positions of the thermocouples being the temperature sensing units
in the mold exerted on estimation accuracy when the estimation of
the solidified state in the mold is performed by using the method
of the present invention.
[0171] A mold with a length of 1090 mm is used, a molten steel
surface level is controlled to be at a position of 85 mm from an
upper end of the mold being a supposed surface level position, and
the continuous casting is performed while setting the casting speed
at 1.7 m/min. The thermocouples are used as the temperature sensing
units, the embedding positions of the thermocouples are set at 20
mm intervals from 15 mm to 255 mm under the molten steel surface
level, in addition, one point is provided at 755 mm under the
molten steel surface level (at 250 mm from a lower end of the mold)
to collect temperature data during casting. Here, the embedding
position of the thermocouple into the mold is represented by a
distance from the molten steel surface level. The collection of the
temperature data is performed while setting a sampling interval to
one second. One thermocouple used for the estimation of the heat
transfer coefficient .beta. and the solidified shell thickness s is
selected from among the plurality of thermocouples, and the
evaluation of the estimation accuracy is performed from estimation
results obtained by different selection ways in nine levels.
[0172] The embedding positions of the thermocouples used for the
estimation of .beta. and s, the estimation accuracy evaluations of
.beta. and s, and a comprehensive evaluation in each level are
illustrated in Table 1. As for the embedding positions of the
thermocouples, .smallcircle. is written for ones used for the
estimation of .beta. and s. Among the nine levels, the most
thermocouples are used in the level "0" (zero), and it is
conceivable that .beta. and s are estimated with the highest
accuracy. The estimation results of the level "0" (zero) are
therefore set as a reference, and relative differences of the
estimation results of .beta. and s in each level are set as
estimation accuracy evaluation indexes. Namely, the estimations of
.beta. and s at the same one minute time zone are performed in each
level, time averages are calculated regarding the estimation values
of .beta. and s at each estimation position disposed in the casting
direction, and a root-mean-square at all estimation positions of
the relative differences for the level "0" (zero) of the time
average of the estimation values of .beta. and s are set as
indexes. As a result, the comprehensive evaluation is set to
.smallcircle. as good estimation accuracy when the relative
differences of .beta. and s are both 10% or less, and the others
are set to .DELTA..
TABLE-US-00001 TABLE 1 .beta. RELA- s RELA- EMBEDDING POSITION OF
THERMOCOUPLE TIVE TIVE (DISTANCE FROM MOLTEN STEEL SURFACE LEVEL)
[mm] DIFFER- DIFFER- COMPREHENSIVE LEVEL 15 35 55 75 95 115 135 155
175 195 215 235 255 755 ENCE ENCE EVALUATION 0 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. 0% 0% .largecircle. 1 .largecircle. -- .largecircle.
-- .largecircle. -- .largecircle. -- .largecircle. -- .largecircle.
-- .largecircle. .largecircle. 1% 2% .largecircle. 2 .largecircle.
-- -- .largecircle. -- -- .largecircle. -- -- .largecircle. -- --
.largecircle. .largecircle. 2% 3% .largecircle. 3 .largecircle. --
-- -- -- -- .largecircle. -- -- -- -- -- .largecircle.
.largecircle. 7% 6% .largecircle. 4 .largecircle. -- -- -- -- -- --
-- -- -- -- -- .largecircle. .largecircle. 21% 11% .DELTA. 5 -- --
-- -- .largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. 10% 5% .largecircle. 6 -- -- -- -- --
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. 13% 6% .DELTA. 7 -- -- -- -- -- -- -- -- -- --
.largecircle. .largecircle. .largecircle. .largecircle. 20% 9%
.DELTA. 8 .largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. -- 24% 4% .DELTA.
[0173] From the level "0" (zero) to the level 4, the solidified
state in mold estimation was performed by selecting the
thermocouples within a range from 15 mm to 255 mm under the molten
steel surface level at an upper side of the mold, and selecting
also the thermocouple at 755 mm under the molten steel surface
level at a lower side of the mold. The thermocouple interval at the
upper side of the mold was changed by each level. The relative
differences of .beta. and s were approximately "0" (zero) % from
the level "0" (zero) to the level 2, and it was indicated that the
thermocouple interval at the upper side of the mold was enough
small. Besides, when the thermocouple interval at the upper side of
the mold was 120 mm, the comprehensive evaluation was 0. FIG. 9 and
FIG. 10 are graphic charts illustrating the typical mold
temperature distribution described in the embodiment and mold
temperature distributions each of which are linearly interpolated
by using the temperatures at the embedding positions of the
selected thermocouples regarding from the level "0" (zero) to the
level 4. Table 2 is one where a root-mean-square in the casting
direction is calculated as for each relative difference between the
typical mold temperature distribution and the mold temperature
distribution which is linearly interpolated by using only the
temperatures at the embedding positions of the thermocouples. Note
that the position at 755 mm under the molten steel surface level
corresponds to the position at 250 mm from the lower end of the
mold, and the temperature reaches a minimum temperature under the
molten steel surface level, and therefore, the temperature at a
position of 550 mm under the molten steel surface level is taken in
the typical mold temperature distribution. There is a high
correlation with the relative difference of .beta. and the relative
difference of s in Table 1, and therefore, it turns out that it is
preferable that the thermocouples are densely embedded at the upper
side of the mold where the temperature gradient is relatively large
so as not to generate a large difference between the mold
temperature distribution which is linearly interpolated by using
the temperatures of the selected thermocouples and the original
mold temperature distribution.
TABLE-US-00002 TABLE 2 ROOT-MEAN-SQUARE LEVEL [%] 0 2.8 1 2.9 2 3.3
3 7.1 4 14.0
[0174] The solidified state in mold estimations were performed
while setting the level "0" (zero) as the reference and without
selecting the thermocouples at the upper side of the mold in each
of the level 5 to the level 7, and without selecting the
thermocouple at the lower side of the mold in the level 8. As a
result, all of the comprehensive evaluations except the level 5
became .DELTA.. It turns out from this result that it is preferable
that an upper end of the range where the thermocouples are densely
embedded is set at within 95 mm under the molten steel surface
level, and the thermocouple is embedded in a vicinity of the
minimum temperature under the molten steel surface level.
Example 2
[0175] The present example is one where performance regarding the
detection of the break-out due to drift using the method of the
present invention was evaluated to compare with conventional
methods. In the present example, the same mold as the example 1 was
used, the positions of the temperature sensing units embedded in
the mold were set to the level "0" (zero) in the example 1, and the
estimation of the solidified state in the mold was performed by
using the temperature data obtained from all of the temperature
sensing units.
[0176] As candidates of the solidified state in mold evaluation
amounts, the amounts given by the expressions (51) to (54) were
employed. Evaluation times were set to 1 minute, 4 minutes, 7
minutes, and 10 minutes, and evaluation points were set to an upper
part, a middle part and a lower part of the mold. An examination
period of the allowable limit values was set to five months, and
the solidified state in mold estimation amounts, the candidates for
the solidified state in mold evaluation amounts, and the casting
conditions were stored as the time-series data. Regarding the
classification of layers of the casting conditions, a grade width
of the casting width was set to 300 mm, a grade width of the
casting speed was set to 0.4 m/min, and a grade width of the
super-heat was set to 10.degree. C., and layer-classified levels
G.sub.01 to G.sub.22 of the casting conditions were set by
combinations of each grade of the casting width, the casting speed,
and the super-heat. Details are illustrated in Table 3.
TABLE-US-00003 TABLE 3 LAYER- CASTING CASTING CLASSIFIED WIDTH
SPEED SUPER-HEAT LEVEL (mm) Vc (m/min) (.degree. C.) G.sub.01 1000
.ltoreq. W < 1300 0.9 .ltoreq. Vc < 1.3 20 .ltoreq. T < 30
G.sub.02 1000 .ltoreq. W < 1300 0.9 .ltoreq. Vc < 1.3 30
.ltoreq. T < 40 G.sub.03 1000 .ltoreq. W < 1300 0.9 .ltoreq.
Vc < 1.3 40 .ltoreq. T G.sub.04 1000 .ltoreq. W < 1300 1.3
.ltoreq. Vc < 1.7 10 .ltoreq. T < 20 G.sub.05 1000 .ltoreq. W
< 1300 1.3 .ltoreq. Vc < 1.7 20 .ltoreq. T < 30 G.sub.06
1000 .ltoreq. W < 1300 1.3 .ltoreq. Vc < 1.7 30 .ltoreq. T
< 40 G.sub.07 1000 .ltoreq. W < 1300 1.3 .ltoreq. Vc < 1.7
40 .ltoreq. T G.sub.08 1300 .ltoreq. W < 1600 0.9 .ltoreq. Vc
< 1.3 10 .ltoreq. T < 20 G.sub.09 1300 .ltoreq. W < 1600
0.9 .ltoreq. Vc < 1.3 20 .ltoreq. T < 30 G.sub.10 1300
.ltoreq. W < 1600 0.9 .ltoreq. Vc < 1.3 30 .ltoreq. T < 40
G.sub.11 1300 .ltoreq. W < 1600 0.9 .ltoreq. Vc < 1.3 40
.ltoreq. T G.sub.12 1300 .ltoreq. W < 1600 1.3 .ltoreq. Vc <
1.7 10 .ltoreq. T < 20 G.sub.13 1300 .ltoreq. W < 1600 1.3
.ltoreq. Vc < 1.7 20 .ltoreq. T < 30 G.sub.14 1300 .ltoreq. W
< 1600 1.3 .ltoreq. Vc < 1.7 30 .ltoreq. T < 40 G.sub.15
1300 .ltoreq. W < 1600 1.3 .ltoreq. Vc < 1.7 40 .ltoreq. T
G.sub.16 1300 .ltoreq. W < 1600 1.7 .ltoreq. Vc 20 .ltoreq. T
< 30 G.sub.17 1600 .ltoreq. W 0.9 .ltoreq. Vc < 1.3 20
.ltoreq. T < 30 G.sub.18 1600 .ltoreq. W 0.9 .ltoreq. Vc <
1.3 30 .ltoreq. T < 40 G.sub.19 1600 .ltoreq. W 0.9 .ltoreq. Vc
< 1.3 40 .ltoreq. T G.sub.20 1600 .ltoreq. W 1.3 .ltoreq. Vc
< 1.7 10 .ltoreq. T < 20 G.sub.21 1600 .ltoreq. W 1.3
.ltoreq. Vc < 1.7 20 .ltoreq. T < 30 G.sub.22 1600 .ltoreq. W
1.3 .ltoreq. Vc < 1.7 30 .ltoreq. T < 40
[0177] On the other hand, when the state in the mold was estimated
from the measurement data of the break-out due to drift being the
abnormal casting which occurred in the past than the examination
period of the allowable limit values, time changes until the
break-out occurrence were as illustrated in FIG. 11 and FIG. 12.
FIG. 11 illustrates the time changes of the short side .beta.
differences of the heat transfer coefficients at the upper part,
the middle part, the lower part of the mold. FIG. 12 illustrates
the time changes of the short side s differences of the solidified
shell thicknesses at the same position.
[0178] The solidified state in mold evaluation amounts are compared
with a normal time by using the abnormal operation cases, and
separation states from the normal time are illustrated in FIG. 13
and FIG. 14.
[0179] FIG. 13 illustrates results obtained from evaluations given
by the expression (55) regarding the expression (51) and the
expression (52) each being the moving average. For example, the
moving average from the past one second to 15 minutes of at least
either of the short side .beta. difference or the short side s
difference is set as the solidified state in mold evaluation
amount.
[0180] FIG. 14 illustrates results where the expression (53) and
the expression (54) are evaluated by the expression (55). From FIG.
14, it turns out that the separation from the normal time is the
largest when the casting state determination amount is set to the
minimum value with sign of the short side s difference at the lower
part of the mold when 10 minutes are set as the evaluation time.
The minimum value may be the minimum value of at least either an
absolute value of the short side .beta. difference or an absolute
value of the short side s difference from past one second to 15
minutes.
[0181] Averages and standard deviations of the casting state
determination amounts by each of the layer-classified levels
G.sub.01 to G.sub.22 of the casting conditions become as
illustrated in FIG. 15 and FIG. 16. The method of the present
invention can be carried out without determining by layers of the
casting conditions, but a trend is different by each layer, and
therefore, it can be seen that the accuracy improves by classifying
by layers.
[0182] FIG. 17 is a prediction value of a ratio where the normal
casting is misjudged to be the abnormal casting relative to the
allowable limit value adjustment constant A, and when A=5, the
ratio goes below an allowable ratio of 0.2%. FIG. 18 is a graphic
chart of the allowable limit values and the casting state
determination amount obtained by the above-stated method in the
break-out due to drift being the abnormal casting in the past, and
it turns out that it is possible to predict at approximately 30
minutes before the break-out occurrence.
Comparative Example
[0183] The detection of the casting failure in the continuous
casting was tried while using the method described in Patent
Literature 6 as a comparative example.
[0184] The mold temperatures were measured by the temperature
sensing units (a first temperature measurement point: 160 mm from
an upper surface of the mold, a second temperature measurement
point: 340 mm) embedded in the mold with intervals in the casting
direction, and the heat flux at an inner surface of the mold at
each measurement point is estimated based on the mold temperature
measurement value by using the heat transfer inverse problem.
[0185] Similar to the example, when a relationship between a
casting elapsed time and a heat flux estimated from the mold
measurement temperature of a broken hole side short side was
examined as for the measurement data of the casting where the
break-out due to drift occurred, the heat flux at the position
exceeded 2.4.times.10.sup.6 W/m.sup.2 at five minutes before the
break-out occurrence to be an ascending trend until the break-out
occurrence, and the heat flux did not decrease to a limit value or
less set in advance as for the first temperature measurement point.
The break-out due to drift occurs because a solidification growth
is inhibited by a heat quantity exceeding a cooling capacity of the
mold locally given to the solidified shell, and the solidified
shell with insufficient strength is pulled outside the mold. It is
therefore conceivable that the calculation result where the short
side heat flux at the broken-hole side increased before the
break-out occurrence was a natural result. However, in Patent
Literature 6, it is supposed that the break-out "occurs because a
portion where a cast slab solidified layer thickness becomes
partially thin is broken due to a foreign substance inserted
between the mold and the cast slab, cracks of the cast slab, and so
on, and molten metal flows out", and it is assumed that "a heat
transfer from the solidified layer to the mold is disturbed by an
effect of the foreign substance or the cracks being causes thereof,
and the lowering of the heat flux occurs", and therefore, detection
objects are only ones whose heat fluxes are lowered. Accordingly,
it is impossible to determine or predict the occurrence of the
break-out due to drift only by applying the method of Patent
Literature 6 as it is.
[0186] Besides, as a relatively easy improved method from the
method in Patent Literature 6, a method is conceivable where it is
predicted that the break-out occurs when the heat flux exceeds a
limit value set in advance (including a case of increasing). As the
limit value set in advance, it was set to 2.7.times.10.sup.6
W/m.sup.2 regarding the first temperature measurement point, and it
was set to 1.9.times.10.sup.6 W/m.sup.2 regarding the second
temperature measurement point. Then the heat flux at the first
temperature measurement point exceeded the limit value 65 seconds
before the actual break-out occurrence, and the heat flux at the
second temperature measurement point exceeded the limit value 26
seconds before the actual break-out occurrence, and therefore, it
was considered that there was a probability of prediction of the
break-out occurrence. However, it was thought that drift leading to
the break-out did not occur during two hours from three hours to
one hour before the break-out occurrence, but there were times
satisfying the above-stated conditions for a total of 77 seconds
divided into eight-times though the break-out did not actually
occur, and the detection resulted in a lot of error. Accordingly,
it turned out that it was difficult to properly predict the
occurrence of the break-out due to drift only by using the method
in Patent Literature 6.
[0187] As stated above, though it was possible to detect the
occurrence of the break-out for some extent, it was impossible to
properly predict the occurrence of the break-out according to the
conventional methods.
[0188] Hereinabove, the detection method of the break-out due to
drift is described, but the casting state in the continuous casting
is one where various physical phenomena complicatedly affect with
each other, and the casting state determination amount proper for
the detection of the break-out due to drift has not been obvious.
Namely, it is considered that the break-out due to drift occurs
because the solidified shell thickness becomes thin, but in
addition, an internal stress or the like of the solidified shell
affects on the occurrence of the break-out, and it cannot be said
that an occurrence mechanism of the break-out due to drift in
itself is enough made clear. Besides, the information obtained by
the measurements is limited. For example, the internal stress of
the solidified shell cannot be directly measured, and it is
necessary to consider a solidified shell shape, a temperature
distribution in the solidified shell, a restriction condition of
the mold if the internal stress is estimated based on the
measurement, but a high-speed calculation method usable in online
is not proposed.
[0189] The present inventors evaluate about various indexes
calculated from the solidified state in mold estimation amounts
estimated by the method of the present invention, and find out the
casting state determination amount capable of detecting the
break-out due to drift with sufficient accuracy to detect the
break-out due to drift with high accuracy under the situation as
stated above.
INDUSTRIAL APPLICABILITY
[0190] The present invention is usable for determining a casting
state in continuous casting where a solidified shell, a mold flux
layer, and a mold exist between a molten steel to mold cooling
water.
* * * * *